The landing phase is a critical phase in the flight of an aircraft, since it is during this phase that most incidents and accidents occur. To facilitate the pilots' task many automatic landing systems have been proposed. In particular the ILS (Instrument Landing System) fitted to large-capacity airliners is well known and its ground infrastructure is present in international airports. MLS (Microwave Landing System) is also available in some European airports. These systems use radio or microwave signals to guide the aircraft in its approach phase both laterally, relative to the axis of the runway, and vertically, relative to the glide path. However, they have the disadvantage that they are not available in all airports, notably due to their high costs, and the fact that they have major usage constraints. In addition, the ground infrastructure has a malfunction probability of the order of 10−3/hour. Aircraft cannot therefore be certain that they will be able to land in automatic mode. More recently automatic landing systems have been produced which use a satellite positioning system called GLS (GPS Landing System), or alternatively SLS (Satellite-based Landing System). Since current satellite positioning systems do not enable the precision required to make a landing to be obtained, these systems must be augmented by ground reference stations such as those of the WAAS (Wide Area Augmentation System) or EGNOS (European Geostationary Navigation Overlay Service) network. The systems are as yet not widespread, and have a relatively low availability rate (of the order of 99.5%) which, again, does not enable landing in automatic mode to be guaranteed permanently.
Due to the spatial and time-related unavailability of such ground infrastructures, attention has turned to autonomous landing systems, using video images of the ground taken by an on-board camera.
These autonomous systems generally use the video images taken by the camera and data relative to the runway to judge the pose of the camera (pose estimation), and to deduce from it the attitude and position of the aircraft relative to the runway. The aircraft's guidance commands are then calculated from the position and the attitude determined in this manner. However, the pose estimate is a complex operation, which generally requires that an on-board digital model of the topography of the airport is available, or at least geometrical and topographical data relating to the landing runway. In addition, when the database containing the digital model is unavailable, or in the event of an emergency landing on a random terrain, the abovementioned autonomous systems are inoperative.
French Patent Application FR-A-2835314, co-owned herewith, discloses a landing assistance system that does not require the features of the landing runway to be known. However, this system operates only when the aircraft is a few meters from the ground and does not enable the aircraft to be guided throughout the final approach, i.e. during the final ten kilometers approximately.
The object of the subject matter disclosed herein is to propose an automatic landing system for an aircraft which is particularly robust, and is able to operate with total or partial absence of data relating to the landing runway, and to guide it autonomously throughout the final approach.